Our invention relates to inductors for power lines and the like, and particularly to such inductors having one or more coaxial coils, each of which carries the desired current.
Inductors are frequently connected in series between electrical switch yards or generating equipment and a relatively high voltage electrical power line for various reasons. One reason is to protect the switch yard and generating equipment from voltage surges such as caused by a lightning strike on the power line. Another reason is to provide a high impedance to carrier frequency signals connected to the power line, so that the carrier frequency signals are not transmitted toward the switch yard or generating equipment and thereby attenuated. But as is readily apparent, since such inductors are connected in series with the power lines, they must carry the full current of the power line. Such a current, even when normal, is large (in the order of hundreds of amperes), so that the inductors must have a large number of conductors capable of carrying such currents, and must have a configuration that can handle and disperse the heat resulting from such current.
Accordingly, a general object of our invention is to provide a new and improved helical inductor for use with electrical power lines.
Another object of our invention is to provide a new and improved inductor that can carry relatively large power frequency currents.
In previous helical inductors for connection in series with power lines, the needed current-carrying capability has been provided by a plurality of coaxial coils connected in parallel. Each coil was designed and wound so that the coil carried the desired magnitude of current for the proper dispersion of the heat generated in and by the coil. This was achieved by coils which were wound with transposed conductors. However, transposed conductors are relatively expensive. As a consequence, coils were wound with untransposed conductors with a precise number of full turns plus a fractional part of a turn. While such a coil with untransposed conductors provided the desired current magnitude in each coil, it also created the problem of terminating each concentric coil at the desired angular position that provided the precise number of turns plus the fractional part of a turn. If there were many coaxial coils, this required a mechanical structure that permitted each coil to be terminated at its desired fractional turn location, or required that there be a mechanical structure which had fewer terminal locations and hence a resultant compromise as to the fractional part of a turn. If the fractional turns are terminated on radial arms which extend from a center common terminal, the radial arms are subjected to considerable mechanical stresses caused by an unintended high current surge resulting from a momentary fault or short circuit on the power line.
Accordingly, another object of our invention is to provide a power line inductor that permits all of the coaxial coils to have the desired number of turns, and to terminate at and be connected to a single common terminal at each end, and still have the electrical characteristics that provide the desired current in each coil.